The present invention relates to substrates, such as may be used for integrated circuit fabrication, micro-machining applications, and similar substrates, and more particularly to cleaving hybrid or composite substrates.
Semiconductor device fabrication technology continues to advance in the pursuit of smaller, faster devices. Integrated circuits devices have become more complex, and in many cases, bigger. New materials and methods are being developed to meet these and other performance requirements. For example, many integrated circuits are fabricated on a silicon xe2x80x9cwaferxe2x80x9d, which was sawn out of a generally round ingot, or boule, and polished on at least one side. Not long ago, silicon wafers typically had a diameter of about 2-4 inches. Then, six inch, and now eight-inch, wafers became commonplace, and the industry is moving toward silicon wafers with a diameter of twelve inches for some applications. The larger diameter wafers can yield more chips per wafer, and improve throughput. Not surprisingly, the larger wafers are generally much more expensive than the smaller wafers.
Many integrated circuit devices are fabricated within a very narrow planar region close to the surface of the wafer. The remainder of the wafer provides mechanical support and may provide other functions, such as impurity gettering or a backside electrical contact.; Thus, the semiconductor material may only need to be of device (i.e. high) quality for a thin region near the surface of the wafer. Epitaxial growth processes have been developed to address this issue. Generally, a thin film of high-purity or other high-quality film of semiconductor material is grown on a substrate, which can be the same material, or a different material, than the grown film. Unfortunately, epitaxial growth processes have not been easy to scale for use with the increased wafer diameters, and yields and throughput have suffered.
Wafer bonding is another process that uses a relatively thin film of semiconductor material. In some instances, a thin film of silicon, for example, is bonded to an insulating substrate, such as silicon oxide, to form a semiconductor-on-insulator (xe2x80x9cSOIxe2x80x9d) structure. Many techniques have been developed to bond one wafer to another, using adhesives, chemical activation, and the like. Some times a bulk wafer of silicon is bonded to an insulating substrate and then the silicon is lapped to the desired thickness, and other times a thin film of silicon is transferred to the insulating wafer.
Other wafer bonding methods have been developed for purposes other than to fabricate SOI substrates, such as transferring a thin film of high-quality semiconductor material onto a semiconductor or other substrate. Alternatively, it may be desirable to produce a thin film of material to form a layer in a micro-electrical-mechanical system (xe2x80x9cMEMSxe2x80x9d) device. Accordingly, a technique and a device for cleaving substrates is desirable for producing a thin film of material to be transferred and/or for separating bonded wafers from each other, and for other purposes.
The present invention provides a method and apparatus for cleaving substrates, including composite substrates.
In one embodiment, a composite substrate of two wafers bonded together has a perimeter notch resulting from an edge-finishing process, typically performed by the wafer manufacturer, of one or both wafers. The edge of a tool, such as a blade, is tapped against the perimeter notch. It is believed the edge applies a wedging force against the two bonded wafers. The edge may rebound after tapping, or preferably, remain wedged in the notch.
A seal is formed around at least the portion of the perimeter notch that was tapped to define a plenum. A gas source is provided to the plenum to pressurize the plenum and separate the substrate into two halves at a selected plane. In a further embodiment, the wafers are held together prior to separation with a selected pressure to facilitate cleaving the wafers while reducing breakage. In a still further embodiment, the pressure applied to the substrate during the cleave process varies across the substrate in a selected fashion.
In another embodiment, a cleaving tool with an edge impinges on a composite substrate at or near a selected plane. The cleaving tool includes a gas port in the edge that provides a source of gas in the region of impingement. The combination of mechanical (solid-to-solid contact) force and gas pressure separate the composite substrate at a selected plane, with or without a perimeter notch formed by the edge finish of the substrates. In a further embodiment, the application of mechanical force triggers the pulse of gas for a source by actuating a valve for a selected period of time. These and other embodiments of the present invention, as well as some of its advantages and features are described in more detail in conjunction with the text below and attached figures.